This invention relates to grease-lubricated rolling bearings used within a wide temperature range, especially grease-lubricated rolling bearings for use in automotive parts provided near an automotive engine such as electric parts and accessories.
A grease-lubricated bearing mounted on an electric part or accessory of an automobile such as an idler pulley or tension pulley is exposed directly or indirectly to radiation heat from the engine, so that its friction surface is heated to about 110.degree. C. The lubricating grease lubricated in the bearing thus is required to be high in high-temperature lubricity and high-temperature durability (or high-temperature life).
In a cold district, such a grease-lubricated bearing may be used at temperatures ranging from -20 to -40.degree.C. Thus, good low-temperature lubricity in addition to high-temperature properties is also required for the grease lubricated in such a bearing.
Conventional grease for bearings that satisfy the above conditions has a worked penetration of 220-310 at 25.degree. C.
One problem with this conventional grease is that it cannot quickly reveal good lubricity inherent to grease if the grease-lubricated bearing is actuated at a low environmental temperature somewhere between 10.degree. C. and -40.degree. C. Thus, immediately after the start, the bearing tends to produce noise.
In the case of a grease-lubricated rolling bearing used in an automotive part, if the automotive engine is started at an environmental temperature of about -40.degree. C., which is not very unusual in winter time in a cold district, the bearing tends to produce noise immediately after the engine is started due to friction between unlubricated sliding surfaces.
This problem of noise in a cold state was not solved by use of a grease having a worked penetration at 25.degree. C. adjusted to 220 to 310.
An object of this invention is to provide a grease-lubricated rolling bearing containing an improved grease which can prevent noise of the bearing immediately after the bearing is actuated even at a minimum environmental temperature expected in a cold district (-40.degree. C.).